This invention relates to an improved system for safely, reliably and automatically transporting persons down from an elevated structure, and in particular to such a system as adapted for use in a fire escape system.
It has long been recognized that a fire escape system which allows persons to be lowered on the outside of a building provides important safety advantages. For example, Blessing U.S. Pat. No. 299,511 and Bixby U.S. Pat. No. 290,961 disclose endless loop ladders mounted to the exterior of a building to serve as fire escapes. The downward movement of the ladders under the weight of individuals on the ladders is limited by friction brakes.
Similarly, Elsner U.S. Pat. No. 1,069,325 discloses an endless loop strap mounted to the exterior of a building. This strap is provided with openings spaced along its length, and a user clips a sling to the openings in order to secure himself to the strap. Once again, friction brakes are used to limit the velocity of the belt.
Cote U.S. Pat. No. 1,206,676, Hill U.S. Pat. No. 2,873,055, and Carlson U.S. Pat. No. 3,325,147 all disclose cable or strap type winding devices for use as fire escapes. The Coat patent discloses the use of a centrifugal friction brake; the Carlson patent discloses the use of a manually operated friction brake; and the Hill patent discloses the use of a hydraulically actuated friction brake. In the Hill patent a positive displacement pump is used to generate a control pressure which varies as a function of the cable speed. This control pressure then actuates a friction brake.
Another approach is disclosed in my previous U.S. Pat. No. 4,402,349 which utilizes a gear track mounted to the side of a building to insure positive engagement between the building and a carriage used to lower individuals to ground level.